Fertilizing your bonsai
The most desirable fertilizer for bonsais must contain three key elements- nitrogen, phosphate and potassium, roughly within the proportion of 5:3:2. Nitrogen will help enhance the growth of the branches, leaves, and the roots. In case your leaves start to turn a yellowish-brown, then you're not applying enough nitrogen. Phosphate will aid in the growth of the branches, leaves, and roots as well, but additionally in the development of the flowers and fruit. Be sure not to apply too much phosphate, especially in the pine or oak species. Lastly, potassium will help assisted in the healthy growth and development of the bonsai tree in general.
There are many different types of fertilizer- liquid, solid, chemical, organic. Personally, i recommend the use of solid organic fertilizer, which is also regarded as the best by most bonsai enthusiasts. Bone meal, rice bran, and oil cake are considered to be probably the most balanced of the common fertilizers. For bonsais in particular, rapeseed cake fertilizer is perfect and really should be accessible in a larger nursery. If you cannot get your hands on rapeseed cake, make use of a mixture of fertilizers within the proportions stated above.